The present invention relates to a cylinder-piston drive, in particular an hydraulically controlled actuator for actuating a gas-exchange valve of an internal combustion engine, having an operating piston, which is displaceable inside a cylinder and which delimits pressure chambers by piston sides facing away from one another. The operating piston may be made up of a plurality of parts and consists of at least two partial pistons, which are placed inside one another, are displaceable relative to one another and are able to strike one another at stop faces. One pressure chamber may be delimited by all partial pistons and the other pressure chamber may be delimited by only a part of the partial pistons. The sliding paths of the partial pistons not delimiting the other pressure chamber are reduced with respect to the overall sliding path of the operating piston, and at least one stop face, arranged on a cylinder, may be provided, which a stop face of one of the partial pistons strikes after traveling the reduced sliding path.
Such a cylinder-piston drive is described in German Published Patent Application No. 101 43 959 and relates to an hydraulically controlled actuator for actuating a gas-exchange valve. The actuator allows the effective areas of the operating piston, which open and/or close the gas-exchange valve, to be modified as a function of its sliding path, so that the actuating force acting on the gas-exchange valve may meet special demands, such as an initially high opening force of the actuator, so that the gas-exchange valve is able to open against the residual gas pressure, or a reduced closing force shortly before the valve closes, for noise and wear reasons.